I really like this boss, and I feel like he's an excellent how-to for a soulsborne boss copy. First phase uses familiar movements, but with a new element in the mix (the fire AoE). Second phase still largely has familiar movements, but with some new moves mixed in there, and still with the fire AoE. And then the third phase is completely new.
However, I really hate how his lava staggers. I get that lava is really deadly, but I'd rather have it deal extremely high damage with no stagger than the current weird stagger locking that it does.